Semiconductor integrated circuit

ABSTRACT

In order to provide a semiconductor IC unit such as a microprocessor, etc., which satisfies both fast operation and lower power consumption properties with its high quality kept, the semiconductor IC unit of the present invention is composed so as to include a main circuit (LOG) provided with transistors, which is formed on a semiconductor substrate, and a substrate bias controlling circuit (VBC) used for controlling a voltage to be applied to the substrate, and the main circuit includes switching transistors (MN 1  and MP 1 ) used for controlling a voltage to be applied to the substrate and control signals output from the substrate bias controlling circuit is entered to the gate of each of the switching transistors and the control signal is returned to the substrate bias controlling circuit.

TECHNICAL FIELD

The present invention relates to a semiconductor IC unit, moreparticularly to a semiconductor IC unit provided with both fastoperation and low power consumption properties.

The present application follows part of the U.S. patent application Ser.No. PCT/JP97/04253 filed on Nov. 21, 1997. The contents of the precedingU.S. patent application are cited and combined with the presentapplication.

BACKGROUND ART

At present, CMOS integrated circuits (IC) are used widely to form asemiconductor IC unit such as a microprocessor, etc. A CMOS IC consumesan electric power in two ways; dynamic power consumption and staticpower consumption. The dynamic power consumption is caused by chargingand discharging at a switching time and the static power consumption iscaused by a subthreshold leakage current. The dynamic power consumptionconsumes a large current in proportion to the square of a supply voltageVDD, so the supply voltage should be lowered to save the powerconsumption of the object CMOS IC effectively. In recent years, thesupply voltage is thus getting lower and lower to cope with such anobject.

On the other hand, some of the power-saving microprocessors available atpresent are provided with a power management feature and its processoris provided with a plurality of operation modes, so that supply of theclock to an active unit is stopped at its standby time according to theset operation mode.

Since the supply of the clock is stopped such way, it is possible toreduce unnecessary dynamic power consumption in such an active unit asmuch as possible. However, the static power consumption caused by asubthreshold leakage current cannot be reduced and still remains on thesame level at this time.

The operation speed of a CMOS circuit drops at a low supply voltage. Inorder to prevent such a speed reduction of a CMOS circuit, therefore,the threshold voltage of the MOS transistor must be lowered inconjunction with the drop of the supply voltage. If a threshold voltageis lowered, however, the subthreshold leakage current increasesextremely. And, as the supply voltage is getting lower, the static powerconsumption increases more remarkably due to the subthreshold leakagecurrent, which has not been so much conventionally. This is why it isnow urgently required to realize a semiconductor IC unit such as amicroprocessor, which can satisfy both fast operation and low powerconsumption properties.

In order to solve the above problem, for example, the official gazetteof Unexamined Published Japanese Patent Application No. Hei-6-54396 hasproposed a method for controlling a threshold voltage of MOS transistorsby setting a variable substrate bias.

The substrate bias is set to the power source potential for PMOS(P-channel MOS transistors) and the ground potential for NMOS (N-channelMOS transistors) in the active state when the object CMOS circuit isrequired for a fast operation. On the other hand, in the standby statein which the CMOS is not required for any fast operation, the substratebias is set to a potential higher than the supply voltage for PMOS andlower than the supply voltage for NMOS (hereafter, this operation willoften be referred to as “applying a bias voltage to a substrate”).

With such a setting of a substrate bias voltage in the standby state, itbecomes possible to raise the threshold level of the MOS transistorscomposing the object CMOS circuit, thereby reducing the static powerconsumption caused by a subthreshold leakage current.

DISCLOSURE OF INVENTION

In order to materialize a semiconductor IC unit such as amicroprocessor, etc., which can satisfy both fast operation and lowerpower consumption properties, the substrate bias must be controlled asdescribed above for each CMOS circuit so that the threshold voltage ofthe MOS transistors is lowered when the semiconductor IC unit is activeand raised when the semiconductor IC unit stands by, thereby reducingthe subthreshold leakage current.

As a result of examination, however, the present inventor has found thatthe following problems still remain unsolved when in controlling thesubstrate bias in an actual semiconductor IC unit.

(1) A substrate bias controlling circuit must be tested easily as ever.

(2) A CMOS circuit must be prevented from malfunction by controlling thesubstrate bias.

(3) An increase of a circuit area must be minimized by controlling thesubstrate bias.

(4) A semiconductor IC unit must be prevented from malfunction when thesubstrate bias is switched over.

In order to solve the above problems, the present invention has proposedthe following means mainly.

To make it easier to test the substrate bias controlling circuit, theoutput of the negative voltage generating circuit is connected to a pad.In other words, the negative voltage generating circuit must be checkedfor if a preset voltage level is reached as its output signal. For thischeck, the negative voltage generating circuit should be provided with aterminal from which the signal is output as it is.

In order to lower the substrate impedance, a plurality of substrate MOStransistors are provided in the main circuit used for controlling thesubstrate bias. The substrate driving MOS transistors are used to drivethe substrate bias when the semiconductor IC unit is active. This isbecause the impedance must be lowered to fix the substrate potential andsuppress the variance of the transistor threshold level when the ICcircuit is active, thereby enabling the respective circuits in the maincircuit to operate.

The driving power of the semiconductor IC unit increases in the activestate more than in the standby state. Preferably, the driving powershould thus be 5 times. Ideally, it should be 10 times that in thestandby state.

Usually, each circuit becomes unstable when the substrate bias isswitched over. In order to prevent this, the gate control signal usedfor controlling the gate voltage of a substrate driving MOS transistoris wired so that the control signal, after being connected to thesubstrate driving MOS transistor, is returned to the substrate biascontrolling circuit and the potential of the returned signal is used bythe substrate bias controlling circuit to detect that the main circuitsubstrate bias is stabilized.

The semiconductor IC unit is provided with a power-on resetting circuit.The power-on resetting circuit detects that the main circuit is powered.The semiconductor IC unit is kept in the active state so that eachsubstrate driving MOS transistor drives the substrate bias shallowly fora fixed time after the main circuit is powered.

While the semiconductor IC unit is shifted from the standby state to theactive state, the substrate bias controlling circuit controls the outputimpedance of the gate control signal so as to become larger than theimpedance to be set after the semiconductor IC unit enters the activestate completely.

The semiconductor IC unit is also provided with a negative voltagegenerating circuit. The substrate bias controlling circuit controls theoutput impedance of the negative voltage generating circuit in thestandby state so as to be smaller than the output impedance in theactive state.

The main circuit comprises a plurality of cells. Those cells compose apower-supply net, which is powered by the first metal levels. Anotherpower-supply net is formed with the second wiring layers, which areorthogonal to the first metal levels. And, a switch cell is disposed ateach intersection point of the power-supply nets formed with the firstand second wiring layers. The power-supply nets of the first and secondwiring layers are connected to each other in the switch cells. Asubstrate driving MOS transistor described above is disposed in each ofthose switch cells.

The substrate bias supply line of a MOS transistor composing one of theabove cells is formed with the first metal levels, which are in parallelto the power-supply net formed with the first metal levels, as well asby the second wiring layers in parallel to the power-supply net formedwith the second wiring layers. In the same way as those power-supplynets, the substrate bias supply line formed with the first metal levelsis connected to the substrate bias supply line formed with the secondwiring layers in each of the switch cells, thereby the gate controlsignal for controlling the gate voltage of each substrate drive MOStransistor is supplied by the second wiring layers above the switchcell, in parallel to the power-supply net formed by the second wiringlayers. The gate control signal is then connected to the gate terminalof the substrate drive MOS transistor in a switch cell described above.

More concretely, the semiconductor IC unit of the present inventioncomprises a main circuit composed of at least one transistor; asubstrate bias controlling circuit used for controlling a voltage to beapplied to each transistor substrate; and a standby controlling circuitused for switching between at least two states; active and standby. Inthe active state, the substrate bias controlling circuit is controlledto increase the subthreshold leakage current flowing in the maincircuit. In the standby state, the bias controlling circuit iscontrolled to decrease the subthreshold leakage current. Thesemiconductor IC circuit is also provided with a negative voltagegenerating circuit, which is incorporated in the substrate biascontrolling circuit, as well as a terminal for outputting a negativevoltage generated from the negative voltage generating circuit toexternal.

At this time, the semiconductor IC unit is provided with a semiconductorchip having output pads, and a package incorporating the semiconductorchip in itself and having external pins, wherein one of the output padsis used as a terminal, which is not connected to any external pin.

In another embodiment, the semiconductor IC unit is provided with a maincircuit composed of at least one MOS transistor, a substrate biascontrolling circuit used for controlling a voltage applied to thesubstrate of the MOS transistor, a standby controlling circuit used forswitching the semiconductor IC unit between at least two states ofactive and standby. The active state allows much subthreshold leakagecurrent to flow in the main circuit and the standby state allows lesssubthreshold leakage current to flow in the main circuit. Thesemiconductor IC unit thus controls the substrate bias shallowly in theactive state and deeply in the standby state, so that the power fordriving the substrate bias shallowly in the active state becomes 10times or over larger than the power for driving the substrate biasdeeply in the standby state.

When the substrate bias is controlled deeply, it should preferably beavoided to operate the main circuit composed of transistors whosesubstrate is applied a bias voltage respectively. When a bias voltage isapplied to the substrate of a transistor, the substrate impedance ishigh. If a MOS transistor is activated, therefore, the substratepotential is easily changed. Consequently, the MOS transistor willprobably malfunction in such a case.

In this embodiment, at least two MOS transistors are used for drivingthe substrate bias shallowly in the active state. Those MOS transistorsare disposed at a distance of 20 μm or over from each other. The gatepotential of each of the substrate driving MOS transistors is controlledby the substrate bias controlling circuit.

The gate control signal used for controlling the gate voltage of thesubstrate driving MOS transistors is returned to the substrate biascontrolling circuit after it is connected to the gate of each of thesubstrate driving MOS transistors. After this, according to thepotential of the returned signal, the substrate bias controlling circuitcan detect that the substrate bias applied to the main circuit isstabilized.

Preferably, the threshold voltage of the substrate driving MOStransistors should be set larger than the threshold level of the MOStransistors composing the main circuit. If the semiconductor IC unit isprovided with an I/O circuit used for interfacing with external, atleast one of the MOS transistors composing the I/O circuit shouldpreferably be coated with an oxidization film thicker than theoxidization film of the MOS transistors composing the main circuit. Suchway, the withstand voltage should preferably be set high at portions towhich a high voltage is applied.

The semiconductor IC unit is further provided with a power-on resettingcircuit used for detecting that the main circuit is powered. The activestate is kept for a fixed time after the main circuit is powered. In theactive state, each substrate MOS transistor drives the substrate biasshallowly.

In another embodiment of the present invention, the semiconductor ICunit is provided with two supply voltages; the first (VDDQ) and thesecond (VDD). The first supply voltage has its absolute value largerthan that of the second supply voltage, which is 2V or under. The secondsupply voltage (VDD) is supplied to the main circuit (LOG) and the firstsupply voltage (VDDQ) is supplied to both substrate bias controllingcircuit (VBC) and standby controlling circuit (VBCC). The first supplyvoltage is applied earlier than the second supply voltage. The substratebias controlling circuit controls so as to keep the main circuit in theactive state for a fixed time after the substrate bias controllingcircuit is applied the second supply voltage.

Furthermore, if the output impedance of the gate control signal of thesubstrate driving MOS transistors in a process in which the state isshifted from standby to active is set higher than that after the stateis already set in the active state, it becomes possible to adjust thespeed for shifting the state from standby to active so as to suppressthe inrush current low in the shifting process.

Furthermore, if the output impedance of the gate control signal of thesubstrate driving MOS transistors in a process in which the state isshifted from standby to active is set higher than that after the stateis already set in the active state, it becomes possible to adjust thespeed for shifting the state from standby to active so as to suppressthe inrush current low in the shifting process. It also becomes possibleto detect by the returned signal that the main circuit is already set inthe active state.

It is also possible to set the amplitude of the gate control signallarger than the gate breakdown voltage of the substrate drivingtransistors.

Furthermore, the semiconductor IC unit is provided with a negativevoltage generating circuit, so that the substrate bias controllingcircuit can control the output impedance of the negative voltagegenerating circuit in the standby state lower than that in the activestate.

Another embodiment of the present invention is a semiconductor IC unitin accordance with claim 13, wherein the negative voltage generatingcircuit is provided with the first and second charging pump circuits, sothat the substrate bias controlling circuit uses the first charging pumpcircuit in the standby state and the second charging pump circuit in theactive state thereby to generate a negative voltage respectively. Inaddition, the pumping capacitor of the first charging pump is setsmaller than that of the second charging pump circuit.

The semiconductor IC unit may also be composed so that the negativevoltage generating circuit can generate the third supply voltage inaddition to the first and second supply voltages so that the firstsupply voltage is larger than the second supply voltage, which is 2V orunder, and the main circuit is supplied the second supply voltage whilethe substrate bias controlling circuit and the standby controllingcircuit are supplied at least the first supply voltage and the substratebias controlling circuit controls the substrate bias of PMOS transistorsso as to be adjusted to the second supply voltage potential in thestandby state and the substrate bias of NMOS transistors so as to beadjusted to the third supply voltage potential thereby to satisfy (thethird supply voltage)=(the first supply voltage)−(the second supplyvoltage).

Furthermore, the negative voltage generating circuit is provided with atleast a charging pump circuit, a comparator, the first reference voltagecircuit used for generating a potential of a half of the second supplyvoltage one, and the second reference voltage circuit used forgenerating an intermediate potential between the first and third supplyvoltages. The comparator compares the voltage output from the firstreference voltage circuit with the voltage output from the secondreference voltage generating circuit thereby controlling at least one ofthe charging pumps to stabilize the third supply voltage.

The first and second reference voltage generating circuits are composedrespectively of a serial circuit in which same type conductor MOStransistors are connected serially. In each of the conductor MOStransistors, the substrate terminal is connected to the source terminaland the gate terminal is connected to the drain terminal. Each of thefirst and second reference voltage generating circuits can be selectedso as to operate a plurality of MOS transistors in a saturation area. Itmay also be composed so as to have Schmitt characteristics.

The main circuit is composed of a plurality of cells. A power-supply netfor those cells is powered by the first metal levels. Anotherpower-supply net is formed with the second wiring layer above thosefirst metal levels so as to be orthogonal to those first metal levels.And, a switch cell is disposed at each intersection point of thepower-supply nets formed with the first and second wiring layers, sothat both power-supply nets formed with the first and second wiringlayers are connected to each other in such the switch cells. Inaddition, a substrate driving MOS transistor is disposed in each ofthose switch cells.

A switch cell may also be composed so as to dispose a decouplingcapacitor between a power source and a ground.

In addition, above the power-supply net formed with the second wiringlayers is disposed a power-supply net formed with the fourth wiringlayers, which are in parallel to the power-supply net formed with thesecond wiring layers. The power-supply nets formed with the second andfourth wiring layers may be connected to each other outside those switchcells.

There is another power-supply net formed with the fifth wiring layers.The power-supply net is connected to the power-supply net formed withthe fourth wiring layers in switch cells. A power source mesh formedwith the power-supply nets of the fourth and fifth wiring layers may berougher than the power source mesh formed with the power-supply netsformed with the first and second wiring layers. And, the fourth andfifth wiring layers may be thicker than any of the first and secondwiring layers.

The substrate bias supply lines of the MOS transistors composing cellsrespectively may be formed with the first metal levels in parallel tothe power-supply net formed with the first metal levels, as well as inparallel to the power-supply net formed with the second wiring layers.Just like the power-supply nets described above, the substrate biassupply lines formed with the first metal levels may be connected to thesubstrate bias supply lines formed with the second wiring layers inswitch cells.

The gate control signal used for controlling the gate voltage of each ofthe substrate driving MOS transistors may be supplied by the secondwiring layers formed above switch cells, which are disposed in parallelto the power-supply net formed with the second wiring layers andconnected to the gate terminal of each of the substrate driving MOStransistors in a switch cell.

The substrate bias supply lines wired by the second wiring layers abovethe switch cells and the gate control may be disposed between thepower-supply nets wired by the second wiring layers above switch cells.

The semiconductor IC unit of the present invention is also provided witha data path circuit. The data flowing direction of the data path circuitmay be in parallel to the power-supply net wired by the first metallevels used for a plurality of cells.

The substrate bias can be set so as to raise the threshold level of atleast one MOS transistor when the semiconductor IC unit of the presentinvention is selected.

In another embodiment of the present invention, in a charging pumpcircuit composed of the first and second pumping capacitors, the firstand second (two) P-channel transistors, the first and second (two)N-channel transistors, and an oscillating circuit, the first pumpingcapacitor, the first P-channel transistor, and the first N-channeltransistor are used for pumping the electric charge of the first pumpingcapacitor when the output of the oscillating circuit is ‘H’ and thesecond pumping capacitor, the second P-channel transistor, and thesecond N-channel transistor are used for pumping the electric charge ofthe second pumping capacitor when the output of the oscillating circuitis ‘L’.

In further another embodiment of the present invention, thesemiconductor IC unit is provided with a main circuit (LOG) includingtransistors composed on a semiconductor substrate respectively and asubstrate bias controlling circuit (VBC) used for controlling a voltageto be applied to each substrate. The main circuit is provided withswitch transistors (MN1 and MP1) used for controlling a voltage to beapplied to each substrate and receives control signals output from thesubstrate bias controlling circuit through the gate of each of theswitch transistors. The control signals may be composed so as to bereturned to the substrate bias controlling circuit.

Each switch transistor is disposed in a rectangular switch cell and eachof other transistors is disposed in a rectangular standard cell. Aswitch cell and a standard cell should preferably be disposed side byside in terms of the layout.

The power sources (VSS and VDD) used for driving the transistors (MN2and MP2) in the main circuit, as well as the power sources (vbp and vbn)of the substrate bias supplied from the substrate bias controllingcircuit should preferably be wired so as to cross both switch cells andstandard cells vertically in the direction those cells are disposed.

The threshold level of the switch transistors should preferably belarger than that of other transistors in terms of the transistorresistance.

The switch transistors (MN1 and MP1) should preferably be insertedbetween the driving power sources (VSS and VDD) for the transistors inthe main circuit and the power sources (vbp and vbn) of the substratebias supplied from the substrate bias controlling circuit in terms ofthe layout.

The source or drain of each transistor can be connected to the drivingpower sources (VSS and VDD) and the transistor substrate potential canbe connected to the substrate bias power sources (vbp and vbn).

The substrate bias controlling circuit can detect that control signals(vbp and vbn), after they are output, have been returned via the maincircuit as control signals (vbpr and vbnr), then have reached apredetermined voltage. Then, the substrate bias controlling circuit cangenerate a detection signal (vbbenbr), thereby stabilizing the operationof the main circuit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a semiconductor IC unit of the presentinvention.

FIG. 2 is a detailed circuit diagram of a main circuit.

FIG. 3 is a circuit diagram of an I/O circuit.

FIG. 4 is a block diagram of each circuit provided in a substrate biascontrolling circuit.

FIG. 5 is operation waveforms of the substrate bias controlling circuit.

FIG. 6 is operation waveforms of the substrate bias controlling circuitin another embodiment of the present invention.

FIG. 7 is a circuit diagram of a VBC 80.

FIG. 8 is a circuit diagram of a VBC 30.

FIG. 9 is an operation waveform of the VBC 30.

FIG. 10 is a circuit diagram of a VBC 85.

FIG. 11 is an operation waveform of the VBC 85.

FIG. 12 is a block diagram of each circuit provided in a VSUBGEN.

FIG. 13 is a circuit diagram of a charging pump.

FIG. 14 is another circuit diagram of the charging pump.

FIG. 15 is a circuit diagram of the VSUBSEN.

FIG. 16 illustrates how switch cells of the present invention aredisposed.

FIG. 17 is a layout of standard cells.

FIG. 18 is a cross sectional view of a standard cell shown in FIG. 17.

FIG. 19 is a layout of switch cells.

FIG. 20 is a cross sectional view of a switch cell shown in FIG. 19.

FIG. 21 is a wiring diagram of a power source and wiring diagrams ofvbp, vbn, cbp, and cbn.

FIG. 22 is a wiring diagram of power source reinforcing lines.

FIG. 23 is a block diagram of wells.

FIG. 24 illustrates how switch cells are disposed in a memory circuit.

FIG. 25 is a cross sectional view of a well.

FIG. 26 is a layout of Deep-N wells.

FIG. 27 is a layout of Deep-N wells and a guard band.

FIG. 28 is a cross sectional view of FIG. 27.

FIG. 29 illustrates how cbpr, cbnr, and VBCR are disposed.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a block diagram of a semiconductor IC unit 100 that uses asubstrate bias controlling circuit of the present invention. VBC is asubstrate bias controlling circuit. LOG is the main circuit whosesubstrate bias is controlled. The LOG is composed of logic circuits andmemory circuits. VBCC is a standby controlling circuit used to controlthe substrate bias controlling circuit. I/O is an I/O circuit used tointerface between the semiconductor IC unit 100 and external. Wiringsbetween circuit blocks, which are not needed specially for substratecontrolling, are omitted here. 109 a and 109 b are substrate drivingcircuits.

The semiconductor IC unit is provided with three types of power sourcesindicated as VDDQ, VDD, and VWELL. VSS and VSSQ are ground potentialsused for VDD and VDDQ. VDDQ and VSSQ are power sources used for the I/Ocircuit. VDD and VSS are power sources used for the main circuit. VWELLis a power source used for the substrate bias controlling circuit VBC.

As shown in FIG. 1, VDD and VSS are also supplied to the substrate biascontrolling circuit VBC. The substrate bias controlling circuit VBCincorporates a negative voltage generating circuit in it, generating anegative voltage VSUB which is inverse in polarity from VDDQ. In thisembodiment, the levels of these supply voltages are assumed as follows;VDDQ=VWELL=3.3V and VDD=1.8V, and VSUB=−1.5V.

101, 102, 103, and 104 are pads of the semiconductor IC unit. The pad102 is supplied 3.3V from VWELL, the pad 103 is supplied 1.8V from VDD,and the pad 104 is supplied 0V from VSS (ground) respectively. 101 is aVSUB pad, but it is used to output a negative voltage generated frominside the substrate bias controlling circuit. The voltage of the pad101 can be monitored to detect errors of the negative voltage generatingcircuit provided in the substrate bias controlling circuit VBC when in awafer test of the semiconductor IC unit 100. Usually, pads 102 to 104are bonded to external pins of the semiconductor IC unit 100, but thepad 101 is not bonded to any outer pin. With this testing method, thenumber of external pins can be saved.

vbbenb is a signal used for starting substrate bias controlling andvbbenbr is a signal indicating that the substrate bias is now beingcontrolled. On the other hand, reset is a RESET signal connected to theRESET signal of the semiconductor IC unit. vbp is a PMOS substrate biasline, vbn is an NMOS substrate bias line, cbp is a PMOS substratecontrol line, cbn is an NMOS substrate control line, cbpr is a PMOSsubstrate control return line, and cbnr is an NMOS substrate controlreturn line. The substrate control return lines cbpr and cbnr are usedfor signals returned after both cbp and cbn signals pass through themain circuit. The same net is used for both of the return lines cbpr andcbnr. In other words, both drive voltages cbp and cbn appear in cbpr andcbnr after a delay. (See FIG. 2 to be shown later.) To each of thesubstrate driving circuits 109 a and 109 b are connected cbp, vbp, cbn,and vbn respectively.

FIG. 2 shows how 6 substrate bias control lines (vbp to cbnr) areconnected in the main circuit LOG. VBCR is a return cell. In this VBCR,the PMOS substrate control line cbp is connected to the PMOS substratecontrol return line cbpr, as well as the NMOS substrate control line cbnis connected to the NMOS substrate control return line cbnr.

ncell is a standard cell. In this embodiment, every ncell is shown as aCMOS inverter composed of PMOS MP2 and NMOS MN2 to simplify thedescription. Of course, every ncell may be more complicated in structurelike a cell composed of a NAND gate, a latch, etc. independently ofothers. The substrate potential of each MOS transistor is connected tovbp for PMOS and vbn for NMOS respectively. Those MOS transistors arecomposing an ncell respectively as shown in FIG. 2.

swcell is a switch cell composed of substrate driving circuits(equivalent to 109 a and 109 b shown in FIG. 1) composed of PMOS MP1 andNMOS MN1, as well as decoupling capacitors CP1 and CP2 respectively. Inthe MP1, the gate is connected to cbp, the drain is connected to VBP,and the source is connected to VDD. Consequently, when the cbp voltageis lower than VDD−Vthp (Vthp: an absolute value of the MP1 thresholdvoltage), MP1 is activated and vbp is driven into the VDD potential(1.8V).

On the other hand, the gate, drain, and source of the MN1 are connectedto cbn, VBN, and VSS (0V) respectively. Consequently, when the cbnvoltage is higher than Vthn (Vthn: an absolute value of the MN1threshold voltage), the MN1 is activated and the vbn is driven into theVSS potential (0V).

Generally, ncell is disposed more than one. So does swcell. The numberof ncells can be increased to integrate complicated circuits in the maincircuit LOG. The number of swcells can also be increased to drive theMP1 and MN1 into a lower impedance respectively when they are activated,as well as vbp and vbn can be driven into VDD and VSS.

In addition to the decoupling capacitor incorporated in a switch cellswcell, another decoupling capacitor can also be incorporated in a spacecell independently of the above one. A space cell means a cell insertedin a space reserved for a wiring area, for example, when standard cellsare to be disposed side by side. If a decoupling capacitor isincorporated in such a space cell, the total capacity of the decouplingcapacitors on the whole chip is increased, thereby reducing the powersource noise more significantly. Since a space cell is a free spaceprovided just in a wiring layer originally, the space is not increasedeven when a capacitor is inserted there.

Both MP1 and MN1 in a swcell must be set to a threshold value higherthan that of a MOS transistor in an ncell. The reason is as follows;although the MOS transistor substrate potential (connected to vbp orvbn) in an ncell is independent of the source potential, the substratepotentials of both MP1 and MN1 in the swcell are always the same as thedrain potential, thereby no substrate bias effect is expected. Asubthreshold leakage current thus flows in the semiconductor IC unit.

For example, if it is assumed that vbp=3.3V, vbn=−1.5V, VDD=1.8V, andVSS=0V are set for NMOS transistors MN1 and MN2 respectively, the sourcepotential S, drain potential D, and substrate potential B of the MN2 inthe ncell become S=0.0V, D=1.8V, and B=−1.5V. Consequently, thethreshold voltage of the MN2 rises due to the substrate bias effect,thereby the subthreshold leakage current is reduced. On the contrary,the source potential S, drain potential D, and substrate potential B ofthe MN1 in swcell becomes S=0.0V, D=−1.5V, and B=−1.5V. Consequently,the substrate bias effect does not work to change the threshold voltage.A large subthreshold leakage current thus flows between VSS and vbn inthe MN1.

There are some methods for setting the threshold voltage levels of bothMP1 and MN1 in the swcell higher than those of the MOS transistors inthe ncell. For example, the concentration of impurity under gate, thegate length (L), or the gate oxidization film thickness is changed.There is no restriction for those methods, but it is assumed in thisembodiment that the gate length L and the gate oxidization filmthickness are changed to obtain a high threshold voltage of both MP1 andNM1. With any of those methods, high voltage MOS transistors can be usedfor the input/output circuit (hereafter, to be referred to as an I/Ocircuit) to/from an external part of the microcomputer.

FIG. 3 shows an embodiment for the I/O circuit. In FIG. 3, only one bitpart of the I/O circuit is shown. The I/O circuit inputs and outputssignals to and from the chip via an input/output terminal PAD. If SEL is‘L’, the PAD functions as an input terminal. If SEL is ‘H’, the PADfunctions as an output terminal. LC1 is a level converting circuit usedto convert a VDD amplitude signal to a VDDQ amplitude signal. The VDDQamplitude is larger than the VDD amplitude. Consequently, a thickoxidization film transistor is provided between the level convertingcell LC1 and the input/output terminal PAD. The thick oxidization filmtransistor is driven by VDDQ. In this embodiment, SEL is set to ‘L’thereby to pull up the PULL using a PMOS pull-up transistor. This isdone only when the PULL must be pulled up. The PMOS is also a thickoxidization film transistor.

At the input side, a VDDQ amplitude signal, entered from external, isconverted to a VDD amplitude signal using an inverter composed of 110Pand 110N. Consequently, these two transistors handle signals whoselevels are not changed yet. Thus, they must be thick oxidization filmtransistors. A resistor 111R, diodes 111D1 and 111D2, and a transistor111 are input protecting circuits. The diodes 111D1, 111D2 may be MOStransistors. The transistors in each of these input protecting circuitsare thick oxidization film transistors.

A higher threshold level voltage can thus be set for thick oxidizationfilm transistors described above, since the transistors do not requireso fast switching speed and handle a voltage higher than the VDD. Thethreshold level voltage can be set higher than that of the transistorsused for ncell. Consequently, it is possible to suppress thesubthreshold current low when such a thick oxidization film transistoris off. Such thick oxidization film transistors can be used for MP1 andMN1 composing a switch swcell shown in FIG. 2 respectively. Noadditional complicated process is needed for MP1 and MN1.

FIG. 4 shows an internal configuration of the substrate bias controllingcircuit VBC. This controlling circuit comprises 4 circuit blocks. VBC 80is supplied powers VDD and VSS, VBC 30 is supplied powers VWELL and VSS,VBC 85 is supplied powers VDD and VSUB and VSUBGEN is supplied VWELL,VDD, and VSS.

Consequently, the supply voltage applied to the circuits in VBC 30, VBC85, and VSUBGEN is 3.3V at most. If VDDQ=VWELL is satisfied, however,the powers supplied to the I/O circuit are VDDQ and VSSQ, the total ofwhich becomes 3.3V. Consequently, the I/O circuit and the substrate biascontrolling circuit can share their devices.

On the other hand, the VBC 80 is powered by 1.8V. Consequently, thesignal lines from VBC 80 to VBC 30 and VBC 85 use a dual rail signal (abalance signal paired by a positive logic signal and a negative logicsignal) respectively. Each signal level is changed (converting a 1.8Vamplitude signal to a 3.3V amplitude signal) in both VBC 30 and VBC 85.

The VBC 80 is an interface circuit block used for interfacing betweensignals cbpr, cbnr, vbbenb, and reset entered from an external part ofthe substrate bias controlling circuit and VBC 30 and/or VBC 85. The VBC30 is a circuit block for controlling the PMOS substrate bias, the VBC85 is a circuit block for controlling the NMOS substrate bias and theVSUBGEN is a negative voltage generating circuit block.

FIG. 5 shows examples of operation waveforms. The main circuit power VDDis activated after the I/O circuit power VDDQ and the substrate biascontrolling circuit VBC power VWELL are activated. Consequently, thenegative voltage generating circuit block VSUBGEN is started thereby togenerate the negative voltage VSUB. On the other hand, if the power VDDis activated, the d_reset signal is asserted for a fixed time. And, ifthis signal is asserted such way, the substrate bias controlling circuittransfers to the state with the highest priority in which the substratebiases of the main circuit are not applied. In other word, the substratebias controlling circuit transfers to the active state. (Applying a biasvoltage to a substrate such way means changing the substrate bias to theVDD potential for PMOS and to the VSS potential for NMOS. And, notapplying a bias voltage to a substrate means changing the substrate biasto a potential higher than the VDD potential for PMOS and a potentiallower than the VSS potential for NMOS.) In this active state, vbp=1.8V,vbn=0V, cbp=0V, cbn=1.8V are set for the PMOS substrate bias line, theNMOS substrate bias line, the PMOS substrate control line, and the NMOSsubstrate control line respectively. Since the substrate control returnlines cbpr and cbnr are used for return signals of cbp and cbn,cbpr=cbp=0V and cbnr=cbn=1.8V is satisfied.

If the d_reset signal is negated with a fixed time passed after the VDDis activated, the substrate bias is controlled by the vbbenb signal. Ifthe vbbenb signal is 3.3V, the standby state is set so that a biasvoltage is applied to the object substrate. If the vbbenb signal is 0V,the active state is set so that no bias voltage is applied to the objectsubstrate.

In other words, if the level of the vbbenb signal is shifted from 0V to3.3V, the state is shifted so that vbp=cbp=3.3V and vbn=cbn=−1.5V aresatisfied. After this, the state is shifted so that cbpr=cbp=3.3V andcbnr=cbn=−1.5V is satisfied. The vbbenbr signal is then shifted to 3.3Vwhen cbpr=3.3V and cbnr=0V are satisfied. Consequently, if the level ofthe vbbenb signal is shifted from 0V to 3.3V, the signal is set to 3.3Vafter a certain time (after the return signals cbpr and cbnr of the cbpor cbn is returned).

If the vbbenb signal is shifted to 0V from 3.3V in level, other signalsare also shifted in level as follows; vbp=1.8V, cbp=0V, vbn=0V, andcbn=1.8V. Then, those other signals are shifted in level as follows acertain time later; cbpr=cbp=0V, cbnr=cbn=1.8V, and vbbenbr=0V. Thevbbenbr functions as a return signal of the vbbenb such way.Furthermore, as shown in FIG. 2, since the substrate potential isdecided by the potentials of both cbp and cbn, it is also possible todetect the substrate potential state by monitoring the vbbenbr obtainedfrom the potentials of both cbp and cbn.

FIG. 6 s hows operation waveforms of the substrate bias controllingcircuit in another embodiment, all of which are different from thoseshown in FIG. 5. As shown in FIG. 6, when the cbp and the cbn arecontrolled, the controlling circuit becomes complicated a little more inconfiguration, but such a complicated controlling circuit enables alarger voltage to be applied to both source and gate terminals of theMP1 and MN2 shown in FIG. 2 respectively in the active state. Both vbpand vbn can thus be driven into a lower impedance. In this case, the cbpand the cbn equivalent to the gate control signal becomes larger inamplitude than the gate breakdown voltage of the substrate drivingtransistors MP1 and MN1. However, as shown in FIG. 6, if both cbp andcbn are changed in level slowly, the voltages between the gate and drainterminals, as well as between the gate and source terminals of both MP1and MN1 become 3.3V at highest, which is equal to the gate breakdownvoltage or under.

Hereunder, a detailed circuit diagram of each circuit block will bedescribed. In order to simplify the description, each of the circuitblocks will be assumed as a circuit generating the waveform shown inFIG. 4.

FIG. 7 shows a circuit diagram of the VBC 80. Numeral 120 is a 2-inputNAND, 121 is a 2-input AND provided with Schmitt characteristics, 122 isan inverter, 123 is a NOR, 124 is a buffer provided with Schmittcharacteristics, and 125 is a buffer provided with a differentialoutput. 126 is a power-on resetting circuit, whose output 127 is chargedto 1.8V from 0V step by step after the power source VDD is activated.Consequently, the 2-input AND 121 outputs 0V for a fixed time, thenoutputs 1.8V. The d_reset signal is thus asserted by this output for afixed time as shown in FIG. 5 when the power source VDD is activated.Although the power-on resetting circuit 126 shown in FIG. 7 is simplycomposed of resistors and capacitors, the circuit 126 can also becomposed in another way if it is possible to detect stabilized powersource VDD.

The signals d_vbbenb, d_cbpr, and d_cbnr are obtained by converting thesignals vbbenb, cbpr, and cbnr to dual rail signals respectively. Thosedual rail signals are used to activate the substrate controlling whenthe power-on state is reset. The d_vbbenbr, which is a dual rail signalused to generate the vbbenbr shown in FIG. 5, is generated from cbpr andcbnr.

FIG. 8 is a circuit diagram of the VBC 30. Numeral 130 is a levelconverting circuit used to generate 3.3V-amplitude signals 133 (VWELL toVSS) from 1.8V-amplitude dual rail signals (VDD to VSS) of both d_vbbenband d_reset signals. A signal 133 enters ‘L’ in the active state or whenthe power-on signal is reset.

Numeral 131 is also a level converting circuit used to generate3.3V-amplitude signals 134 (VWELL to VSS) from 1.8V-amplitude dual railsignals (VDD to VSS) of both d_cbpr and d_reset signals. A signal 134becomes 0V when the signal cbpr is 0V or when the power-on signal isreset. If a signal 133 becomes 0V in level, the signal vbp enters thehigh impedance state and both cbp and cbpenbr become 0V. If the signalcbp becomes 0V, the MP1 in every swcell in the main circuit is activated and the signal vbp is driven into 1.8V.

Numeral 132 is also a level converting circuit used to output the signald_vbbenbr from th e VBC 80 shown in FIG. 7 as a 3.3V-amplitude signalvbbenbr.

FIG. 9 shows how the signal level of cbp is changed. The outputimpedance of the cbp is changed in two steps. The cbp is driven by theinverter 135 controlled by a signal 133. If both signals 133 and 134 are0V, the NMOS 136 is activated, thereby the cbp is driven. In thisembodiment, the gate width of the NMOS 136 is set more wider than thatof the NMOS in the inverter 135. If the semiconductor IC unit enters theactive state and the signal 133 becomes 0V, then the inverter 135 drivesthe cbp into 0V. However, since the cbp is wired in the whole maincircuit and it is provided with a large load capacity, the cbp is driveninto 0V slowly. This shift of the cbp is detected according to a shiftof the signal cbpr, which is a return signal of the cbp. The signald_cbpr is thus changed in level. Consequently, the signal 134 is driveninto 0V and the NMOS 136 is activated. Consequently, the cbp is driveninto 0V at a low impedance. Such way, the cbp is driven at a lowimpedance in the active state and less affected by a noise caused by anoperation of the main circuit. And, if the cbp is driven into 0V, theMP1 in every swcell in the main circuit is activated. If the cbp isdriven into 0V slowly as shown in FIG. 8(B), however, the MP1 in everyswcell can be protected significantly from a simultaneous switchingnoise.

FIG. 10 shows a circuit diagram of the VBC 85. 140 is a level convertingcircuit used to generate 3.3V-amplitude signals 142 (VDD to VSUB) from1.8V-amplitude dual rail signals (VDD to VSS) of both d_vbbenb andd_reset signals. A signal 142 becomes 1.8V in the active state or whenthe power-on signal is reset.

141 is also a level converting circuit used to generate 3.3V-amplitudesignals 143 (VDD to VSUB) from 1.8V-amplitude dual rail signals (VDD toVSS) of both d_cbnr and d_reset signals. A signal 143 becomes 1.8V whenthe signal cbnr is 1.8V or when the power-on signal is reset. If asignal 142 is driven into 1.8V, the signal vbn enters the high impedancestate and the signal cbn is driven into 1.8V. If the signal cbn isdriven into 1.8V, the MN1 in every swcell in the main circuit isactivated. The signal vbn is thus driven into 0V.

FIG. 11 shows how the cbn is shifted. The output impedance of the cbn ischanged in two steps just like the cbp. The cbn is driven by theinverter 144 controlled by the signal 143. When the signal 142 is 1.8Vand the signal 143 is 1.8V, however, the PMOS 145 is activated, therebyit is also driven by the PMOS 145. In this embodiment, the gate width ofthe PMOS 145 is set larger than the gate width of the PMOS in theinverter 144. If the semiconductor IC unit is shifted into the activestate and the signal 142 is driven into 1.8V, the inverter 144 drivesthe cbn into 0V. However, the cbn is wired in the whole main circuit andits load capacity is large. Therefore, the cbn is driven into 0V slowly.This shift is detected according to a shift of the return signal cbnr ofthe cbn, thereby the signal d_cbnr is changed in level. This drives thesignal 143 into 1.8V and the PMOS 145 is activated. Consequently, thecbn is driven into 1.8V at a low impedance. Such way, when thesemiconductor IC unit is active, the cbn is driven at a low impedancejust like the cbp, thereby the semiconductor IC unit can be protectedeffectively from noise caused by the operation of the main circuit. Ifthe cbn is driven into 1.8V, the MN1 in every swell in the main circuitis activated. If the cbn is driven into 1.8V slowly as shown in FIG. 11,however, the simultaneous switching noise of the MN1 can be reduced inevery swell.

As described above, according to the substrate bias controlling methodof the present invention, the substrate driving impedance is smaller inthe active state in which no bias voltage is applied to each substrate(the substrate is driven by every swell) than in the standby state inwhich a bias voltage is applied to each substrate (the substrate isdriven by VBC). Consequently, if the semiconductor IC unit is shiftedinto the active state when it is powered as described above, it ispossible to avoid problems of an increase of a current, owing tounstableness of the substrate potential, that goes through power sourcesat a power-on time, as well as a latch-up problem. In addition, althoughthe substrate noise is increased by the operation of the main circuit inthe active state, the noise can be reduced thereby preventing the maincircuit from problems such as malfunction, latch-up, etc., if thesubstrate driving impedance is suppressed low.

FIG. 12 shows an internal configuration of the negative voltagegenerating circuit VSUBGEN. The circuit is composed of three circuitblocks. VSUBSEN is a substrate bias sensing circuit, PMP1 is a chargingpump circuit 1, and PMP2 is a charging pump circuit 2. The substratebias sensing circuit VSUBSEN monitors the VSUB potential, as well asboth active and standby states using the signal vbpenb. And accordingly,PMP1 and PMP2 can be controlled using control signals pmp1enb andpmp2enb so as to satisfy VSUB=VDD+VSS−VWELL.

PMP1 is started when the signal pmp1enb is asserted and PMP2 is startedwhen the signal pmp2enb is asserted. The pumping capacity makes adifference between PMP1 and PMP2. PMP1 has a pumping capacity largerthan that of PMP2. The signal vbpenb choose to use between PMP1 or PMP2.PMP2 is used in the active state and PMP1 is used in the standby state.

The VSUB potential is used only in the substrate bias controllingcircuit when the semiconductor IC unit is in the active state. Thus, somuch current does not flows into the VSUB. Consequently, the PMP2, whosepumping capacity is small, is used. In the standby state, the VSUBpotential is supplied to the whole main circuit. Such a current as ajunction current, etc. thus flows into the VSUB. Consequently, the PMP1,whose pumping capacity is large, is used.

FIG. 13 shows a circuit diagram of the charging pump 1 PMP1 of thepresent invention. OSC is a ring oscillator, which ocillates to chargethe VSUB to a negative voltage only when the signal pmp1enb is asserted.

FIG. 14 shows a circuit diagram of a charging pump obtained by addingPMOSs 162 and 163 to a charging pump circuit described in “VLSI memory(p266)” written by Kiyoo Ito and published by Baifukan. The chargingpump charges the VSUB using PMOSs 160 and 162 twice during one cycleoscillation of the ring oscillator. According to the present invention,NMOSs 164 and 165 are further added to the charging pump as shown inFIG. 13. Consequently, the VSUB is less affected by the threshold levelsof both PMOSs 160 and 161, so that the VSUB can function satisfactorilyeven at a low voltage operation. When VWELL is 3.3V, the configurationshown in FIG. 14 can obtain only VSUB=−3.3+vthp (vthp=absolute thresholdlevel of both PMOSs 160 and 161); it would be VSUB=−2.3V at highest. Onthe contrary, according to the method of the present invention, it ispossible to reach VSUB=−3.3V or so.

No circuit diagram is shown specially for the charging pump circuit 2PMP2 in this embodiment. However, the capacity of each of the PMOSs CP3and CP4 used as capacitors in FIG. 13 can be reduced thereby to reducethe capacity of each of the capacitors. Of course, the sizes of otherMOS transistors can be optimized to be suited for this CP3 or CP4.

FIG. 15 shows a circuit diagram of the substrate bias sensing circuitVSUBSEN. VREFGEN is a reference voltage generating circuit used toobtain an output of VREF=(VDD−VSS)/2 from NMOS transistors 150 and 151connected serially. V1GEN is a VSUB potential sensing circuit used toobtain an output of V1=(VWELL−VSUB)/2 from the NMOS transistors 152 to155 connected serially. The circuit is composed so that about 1V isapplied to between the source and drain of each NMOS transistor, as wellas the gate is set long. Consequently, it becomes possible to suppressthe continuous current from VDD to VSS or from VWELL to VSUB low. Inaddition, since the circuit is operated in a saturation area, thecircuit can obtain VREF or V1 insensitively to a variance. Furthermore,the present invention uses NMOS transistors, not PMOS transistors. NMOStransistors are excellent in saturation characteristics more than PMOStransistors. The circuit can thus obtain VREF or V1 insensitively to avariance among NMOS transistors even when only about 1V is applied tobetween source and drain.

AMP1, AMP2, and AMP3 are differential amplifiers, which are combined tocompose a differential amplifier. The differential amplifier composed ofAMP1, AMP2, and AMP3 receives VREF and V1, and when in at VREF<V1,pmp1enb or pmp2en is asserted. Consequently, VSUB is charged to anegative voltage. When in VREF>V1, pmp1enb or pmp2enb is negated. SinceVSUB causes a leakage current toward VSS, VWELL, and VDD, if bothpmp1enb and pmp2enb are negated, VSUB is discharged to a positivepotential. This pmp1enb or pmp2enb is asserted and negated repetitively,so that V1=VREF, that is, VSUB=VDD−VWELL is kept. If vbpenb is 3.3V(standby state) as described above, the pmp1enb is asserted. If vbpenbis 0V (active state), the pmp2enb is asserted.

A feed-back path is formed between AMP1 and AMP2. The differentialamplifier composed of AMP1, AMP2, and AMP3 is thus provided withhysteresis characteristics. The hysteresis characteristics mentionedhere means a change of the differentiating point of a differentialamplifier, caused by an output of the amplifier. In other words, itmeans Schmitt characteristics. Consequently, it is prevented thatpmp1enb or pmp2enb is asserted/negated many times repetitively aroundV1=VREF, thereby to prevent an increase of the power consumption.

Furthermore, the operation current of the differential amplifier ischanged within AMP1 to AMP3 between when vbpenb is asserted and when itis negated. In the standby state when vbp is asserted, the vbn of themain circuit is connected to the VSUB. This means that a large substratecapacity is connected to the main circuit. The level of the VSUB is thuschanged slowly. Since no fast operation is needed between AMP1 and AMP3,the operation current can be limited so that the power consumption isreduced in a process from AMP1 to AMP3. On the other hand, in the activestate when the vbp is negated, only the substrate bias controllingcircuit VBC is connected to the VSUB. This means that a comparativelysmall capacity is connected to the VSUB. Consequently, the level of theVSUB is changed quickly, so that a fast operation is needed in a processfrom AMP1 to AMP3. In the active state, the power consumption is not sohigh. A large operation current is thus set in the process between AMP1and AMP3 for enabling fast operations.

Hereunder, the substrate bias powering method will be described indetail in an embodiment of the present invention.

FIG. 16 shows a layout of both ncells and swcells. The swcells aredisposed continuously in the vertical (Y) direction. Both swcells andncells are aligned in height. In the horizontal (X) direction, theswcells are disposed at variable pitches L within a certain value. Ofcourse, those cells can be disposed at equal pitches, but varying thepitches would increase the freedom of the layout. In any way, the pitchL can be decided considering the following items.

(1) Power line impedance

(2) Power wiring migration

(3) substrate noise generated in vbp and vbn according to the operationof ncells

FIG. 17 shows an internal layout of an ncell. Just as in the case shownin FIG. 2, an inverter is taken as an example. The vbp, the vbn, theVDD, and the VSS are powered by the first layer metallic wiringconsisting of four lines disposed in parallel (hereafter, to bedescribed as M1). The vbp and the vbn are also powered by the surfacehigh density layer respectively. H is a cell height, indicating a basicrepetition unit in the vertical (Y) direction. The ncells are disposedin the vertical (Y) direction so as to be mirror images of each otherwith reference to this height. Consequently, both vbp and vbn can beshared by ncells adjacent at vertical positions, reducing the ncellarea.

FIG. 18 shows a cross sectional view of FIG. 17 at the A-B line. N-wellis an N-well used for forming MP2 and P-well is a P-well for formingMN2. Deep-N is an N-well disposed deeper than N-well and P-well. Inother words, the ncell has a 3-layer well structure.

FIG. 19 shows an internal layout of an swcell. H is a cell height justas in the case of the ncell. The vbp, the vbn, the VDD, and the VSS arepowered by M1 in the same way as those of the ncell. As shown in FIG.16, the swcells are disposed continuously in the vertical (Y) direction.Horizontally, those cells are disposed at pitches restricted within acertain value. With such a disposition, it becomes possible to makewiring of power reinforcing lines at the swcell places. In FIG. 19, thesecond layer metallic lines disposed in parallel in the verticaldirection are two power reinforcing lines. Between these two powerreinforcing lines are disposed two reinforcing lines vbp and vbn and twoother lines cbp and cbn. The power reinforcing lines VDD and VSS at bothends are effective to protect the four substrate bias control lines fromexternal noise.

MP1 is formed with 6 separated transistors. The gate, drain, and sourceof each transistor in the MP1 are connected to cbp, vbp, and VDDrespectively. MN1 is formed with 3 separated transistors. The gate,drain, and source of each transistor in the MN1 are connected to cbn,vbn, and VSS respectively. Each of the decoupling capacitors CP1 and CP2is divided into two transistors. The transistors of both CP1 and Cp2 arepositioned at both ends of the MP1 and MN1 respectively. The capacity ofeach of CP1 and CP2 is generated using a MOS gate capacity.

The ratio of the decoupling capacitors CP1 and CP2 to those of MP1 andMN1 is not limited specially. In an extreme example, one or both of thedecoupling capacitors CP1 and CP2 are omissible. Power noise can bereduced with a decoupling capacitor if its size is increased. On theother hand, if MP1 and MN1 are increased in size, the substrate bias canbe connected to a power source at a lower impedance when themicroprocessor is in the normal state so as to be protected moreeffectively from noise, as well as from a latch-up trouble.

The VIA holes formed between the VDD lines of M1 and M2, as well as theVIA holes formed between the VSS lines of M1 and M2 are omitted here tosimplify the description. A VIA hole can be formed at each intersectionpoint of the wiring.

FIG. 20 shows a cross sectional view of FIG. 19 at the A-B line. Just asshown in FIG. 18, P-well is a P-well for forming the MN1 and Deep-N isan N-well disposed deeper than the P-well. The swcell thus comes to havea so-called 3-layer well structure. In this case, VIA holes, which areomitted in FIG. 19, are illustrated actually between the VSS lines ofboth M1 and M2. As shown in FIG. 2, a thick oxidization film transistoris used for MN2 so as to raise the threshold level.

FIG. 21 shows a concrete example for how to wire the power lines VDD andVSS, as well as substrate bias control lines vbp, vbn, cbp, and cbn. Thelayout of power lines shown in FIG. 21 is obtained by adding the abovelines to the layout shown in FIG. 16. In the horizontal (X) direction,VDD, VSS, vbp, and vbn are wired with M1 in parallel to each other. Asshown in FIG. 17, the vbp is shared by two cells disposed verticallywith the vbp therebetween. And, two VDD lines are laid in parallel aboveand under of those two cells. The vbn is also shared by two cellsdisposed vertically with the vbn therebetween. And, two VSS lines arelaid in parallel above and under those two cells. Of course, both VDDand VSS lines can be thicker than vbp and vbn lines.

As shown in FIG. 19, VDD, VSS, vbp, vbn, cbp, and cbn wired with M2 aredisposed on the swcells in the vertical (Y) direction. VDD, VSS, vbp,and vbn are connected to each other like a mesh at intersection pointsof M1 and M2.

FIG. 22 shows how power sources VDD and VSS are reinforced. The powersource lines VDD and VSS formed with the fourth and fifth metallicwiring layers (M4 and M5) are wired like a mesh in accordance with thebasic repetition unit shown in FIG. 21.

Above the VDD and VSS formed with M2, which are wired in the vertical(Y) direction, are wired both VDD and VSS formed with M4. And, in orderto connect those VDD and VSS to each other, the third metallic wiringlayer (M3) is needed. If those VDD and VSS are connected at everyswcell, the M3 is wired vertically. This will arise a problem that no M3path is formed in the horizontal (X) direction, however.

In FIG. 22, M2 and M4 power lines are connected every three swcellsshown as swcell2 or swcell3. With this connection, M3 wiring paths canbe secured in the horizontal (X) direction.

The M5 power line is wired only on every 6 swcells shown as swcell3. TheM5 power line is thus connected to the M4 line at each swcell3, which isan intersection point of M5 and M4.

As described above, the fine pitch power source meshes of M1 and M2 arereinforced by the rough pitch power source meshes of M4 and M5, therebyto lower the impedance of each of the VDD and VSS power source lines.

Although each of the M4 power source lines in the vertical direction iswired at every swcell, the line may also be wired roughly every two orthree swcells. Although the impedance of each of the power source linesincreases, this wiring method makes it possible to secure M4 paths inthe vertical direction.

FIG. 23 shows the relationship between swcells and wells disposed asshown in FIG. 22. P-wells and N-wells are disposed alternately likebelts so that two ncells share one well.

FIG. 24 shows a layout of both memory circuit swcells and power sourcelines. In FIG. 24, none of word and bit lines is illustrated, but wordlines are disposed actually in the horizontal (X) direction and bitlines are disposed actually in the vertical (Y) direction respectively.The memory mat power source lines wired horizontally in the memory cellsare reinforced by the power lines 200, 201, and 202 provided at bothends thereof. Numeral 203 is a power line for supplying an electricpower to each of word drivers and decoders. 204 is a power line forsupplying an electric power to each sense amplifier. Cells swcell aredisposed for each of the power lines 200 to 204 as shown in FIG. 24.

Usually, only one or two of a plurality of word drivers and a pluralityof word decoders work simultaneously. Consequently, substrate noise isnot generated so much. This is why only two swcells are disposed at bothends of the power line 203 as shown in FIG. 24.

On the contrary, many sense amplifiers work simultaneously. However, thepotentials inside the sense amplifier are set so that the number ofnodes in which the level is shifted from ‘L’ to ‘H’ and the number ofnodes in which the level is shifted from ‘H’ to ‘L’ becomes almostequal. Consequently, even when many sense amplifiers worksimultaneously, substrate noise is not generated so much. In this case,swcells are disposed at positions other than both ends of the power line204 shown in FIG. 24, thereby effective to reduce substrate noise.

There will be considered many other methods for how to dispose swcells.In short, however, what is important is only that many more swcellsshould be disposed on the same well according to how many devices willrun simultaneously on the same well. It is also possible to evaluate thechange of a diffusion layer existing in a well by |NH−NL|/NA (NH=thearea of the diffusion layers except for the diffusion layer connected toa power source, NH=the area of a diffusion whose potential is changedfrom ‘H’ to ‘L’, NL=the area of a diffusion layer whose potential ischanged from ‘L’ to ‘H’), then decide the number of swcells, the pitchesL of swcells, and the size of MOS transistors in a swcell with referenceto the evaluation result. In short, what is needed is just minimizingthe |NH−NL|/NA value.

For example, for a circuit that has a regular data flow such as a datapath, it is only needed to control so that data flows in the X directionshown in FIG. 22 in the data path. Since the cells that are operatedsimultaneously are distributed into a plurality of wells, the above|NH−NL|/NA is reduced.

FIG. 25 shows a cross sectional view of a semiconductor IC unit of thepresent invention. As shown in FIG. 18, the Ns shown as 302, 304, 306,308, and 310 are the same as an N-well respectively used to form a PMOStransistor. The Ps shown as 301, 303, 305, 307, 309, and 311 are thesame as a P-well respectively used to form an NMOS transistor. TheDeep-Ns shown as 312 and 313 are N-wells formed at deeper positions thanNs and Ps. The semiconductor IC unit has a “triple well structure”.

The Deep-Ns 312 and 313 are separated electrically by a p-substrate 310and a P-well 307. Consequently, the substrate potential of the MOStransistors A formed on 302, 304, 306, 308, and 310 can be decidedindependently of the substrate potential of the MOS transistors B formedon 301, 303, 305, 307, 309, and 311, and vice versa. In addition, thenoise, etc. generated from the MOS transistors A can be suppressed so asto effectively protect the MOS transistors B from its influence.

FIG. 26 shows the Deep-N structure of the semiconductor IC unit of thepresent invention. CPG is a clock controller and it includes analogcircuits such as a PLL (Phase Locked Loop), etc. TLB is an addressconverter and CACHE is a cache memory. CPU is a central processing unit,FPU is a floating-point arithmetic unit, LOG1 is a random logic 1, LOG2is a random logic 2, and PAD is an I/O unit. Each circuit block isformed such way on a Deep-N different from others.

As shown in FIG. 25, it is possible to reduce the influence of a noisegenerated in each circuit block to be exerted on other blocks. Forexample, since PAD drives external pins with a larger amplitude than theinternal signal amplitude, it generates much noise. This noise can beprevented from exerting on analog circuits such as a CPG, etc.

Furthermore, since a substrate potential can be applied to each blockindependently of others, it is possible to dispose circuits whosesubstrate is not controlled by any of vbp, vbn, cbp, and cbn in LOG2. Inother words, it is possible to dispose a circuit in which a power sourceis connected to the substrate potential (VDD=vbp, VSS=vbn) in the LOG2.

FIG. 27 shows a guard band disposed between Deep-Ns. A guard band gband1is thus disposed between the Deep-Ns as shown in FIG. 27.

FIG. 28 shows a cross sectional view of the guard band shown in FIG. 27.A P-well 307 provided between Deep-Ns is then grounded to the VSSpotential through the P+ diffusion layer 314. This makes it possible tofurther reduce the transmission of a noise between the Deep-Ns. Forexample, the substrate noise generated in a MOS transistor on the P-well305 is transmitted to the Deep-N 312 due to a capacitive coupling, sincethe impedance of the Deep-N 312 is not so low. And, when this noise isto be transmitted to the p-substrate 300 due to the capacitive couplingin the same way as in the above case, the p-substrate is fixed to theground potential by a guard band at a low impedance. The noise, whenappearing on the p-substrate, is thus reduced. Such way, it issuppressed effectively for the noise generated from the MOS transistorsformed on 302, 304, 306, 308, and 310 to be transmitted to the MOStransistors formed on 301, 303, 305, 307, 309, and 311.

FIG. 29 shows layout images of both cbp and cbpr on a semiconductor ICunit and the position of the return cell VBCR shown in FIG. 2. Thedescription of both cbn and cbnr will be omitted here, since it is thesame as that of both cbp and cbpr. The vbp and the vbn are wired like amesh, since swcells are disposed side by side as shown in FIG. 21.However, the cbp and the cbn are not wired like a mesh; they are wiredlike stripes. FIG. 29 shows swcells disposed and connected so as toshunt the stripe-like wiring. And, a return cell is used to returnentered cbp and cbn to the substrate bias controlling circuit VBC ascbpr and cbnr. A return cell is thus disposed so that cbpr is returnedat a later timing than the arrival of the cbp of the swcell whosetransmission time for cbpr is the latest among the swcells. For example,such a return cell should be disposed farthest from the substrate biascontrolling circuit VBC.

In the above embodiment, the potential to be applied to the substratebias is 1.8V or 0.0V in the active state and 3.3V or −1.5V in thestandby state. The potential value can be varied freely. In the activestate, a proper potential can be applied to the substrate bias therebyto adjust the variance of the threshold level of the MOS transistors.

The main circuit can also be divided into a plurality of circuit blocks,so that each of those circuit blocks is provided with a controllingcircuit such as VBC 30, VBC 85, etc., thereby each circuit block isprovided with active and standby states. Each circuit block can thus becontrolled so that other idle circuit blocks are set in the standbystate. Consequently, power consumption can be controlled for thesemiconductor IC unit of the present invention more effectively indetail. In some circuit blocks, it is no need to apply a bias voltage tothe substrates respectively even in the standby state. For example, itis such a case that an object circuit block is composed of MOStransistors whose threshold level is high and the subthreshold leakagecurrent can be neglected.

According to the above embodiment, the threshold level of the MOStransistors is set low in the active operation mode and high in thestandby operation mode of the semiconductor IC unit respectively.However, the bias voltage to be supplied to the substrate can be set sothat a high threshold level is assumed for an IDDQ test as described in1996 IEEE SPECTRUM (pp. 66-71).

If a high threshold level is assumed, the substrate should be applied alarger substrate potential for an IDDQ test than the substrate potentialapplied in the standby mode. In other words, PMOSFET should be applied ahigher potential than that in the standby mode and NMOSFET should beapplied a lower potential than that in the standby mode. This enables toreduce the subthreshold leakage current that flows at an IDDQ test,improving the accuracy of trouble locating.

In order to enable such the operation, the VWELL potential is increased,for example, from 3.3V to 4.0V and the VSUB potential is lowered from−1.5V to −2.2V for an IDDQ test. For a circuit, however, a propermeasure should be taken to prevent a through-current from flowing in anobject circuit even the VWELL potential is set differently from the VDDQpotential. For this purpose, all the signals to be transmitted to thesubstrate bias controlling circuit must be level-downed in the VBC 80,then their potential must be converted to the VWELL or VSUM potentialbefore use. The object circuit should be provided with a buffer used forsuch a voltage to realize the above operation.

According to the above embodiment, the substrate structure is composedof 3 well layers. The structure can be varied, for example, to aso-called twin-tab 2-well structure or an SOI (Silicon on insulator)structure.

Furthermore, as shown in FIGS. 17, 19, and 21, M1 supplies a substratebias power in cells. This structure can be varied, however. For example,such a power can also be supplied from a diffusion layer or asilicide-transformed diffusion layer as described in 1997 Symposium onVLSI circuits Digest of Technical Papers, pp. 95-96.

The explanation of reference symbols in the drawings of the presentapplication is written together in the following.

VBC: Substrate bias controlling circuit, LOG: Main circuit, VBCC:Stand-by controlling circuit, I/O: I/O circuit, vbbenb: Substrate biascontrolling start signal, vbbenbr: Substrate bias controlling-nowsignal, vbp: PMOS substrate bias line, vbn: NMOS substrate bias line,cbp: PMOS substrate controlling line, cbn: NMOS substrate controllingline, cbpr: PMOS substrate control return line, cbnr: NMOS substratecontrol return line, AMP1 and AMP2: Differential amplifier, AMP3:Schmitt input differential amplifier, VBCR: Return cell, swcell: Switchcell, ncell: Standard cell, P-sub: P-substrate, PLL: Phase locked loop,CPG: Clock controller, TLB: Address transformer, CHCHE: Cache memory,CPU: Central processing unit, FPU: Floating-point arithmetic unit, PAD:I/O unit.

INDUSTRIAL APRICABILITY

As described above, the present invention can provide a semiconductor ICunit, such as a microprocessor, etc., which can satisfy the followingrequirements with respect to fast operation and lower power consumptionproperties:

(1) it is easy to test the substrate bias controlling circuit.

(2) it is possible to prevent each CMOS circuit from malfunction bycontrolling the substrate bias.

(3) it is possible to minimize an increase of each circuit area bycontrolling the substrate bias.

(4) it is possible to prevent the semiconductor IC unit from malfunctionwhen the substrate bias is changed over.

What is claimed is:
 1. A semiconductor IC unit comprising; a maincircuit including transistors formed on a semiconductor substrate and asubstrate bias controlling circuit used for controlling a voltage to beapplied to said substrate, wherein said main circuit includes a switchtransistor used for controlling a voltage to be applied to saidsubstrate; a control signal output from said substrate bias controllingcircuit is entered to the gate of said switch transistor and saidcontrol signal is returned to said substrate bias controlling circuit.2. A semiconductor IC unit in accordance with claim 1, wherein saidswitch transistor is disposed in a rectangular switch cell and saidtransistor is disposed in a rectangular standard cell, and said switchcell and a plurality of standard cells are disposed side by side in aline.
 3. A semiconductor IC unit in accordance with claim 2, wherein thewiring of a driving power source used for driving transistors of saidmain circuit and the wiring of said substrate bias power source suppliedfrom said substrate bias controlling circuit are crossing said switchcell and a plurality of standard cells vertically in the direction inwhich said cells are disposed.
 4. A semiconductor integrated circuit inaccordance with claim 1, wherein a threshold of said switch transistoris larger than a threshold of said transistor.
 5. A semiconductor ICunit in accordance with claim 1, wherein said switch transistor isinserted between said driving power source used for driving transistorsof said main circuit and said substrate bias power sources (vbp and vbn)supplied from said substrate bias controlling circuit.
 6. Asemiconductor IC unit in accordance with claim 5, wherein the source ordrain of said transistor is connected to said driving power source andthe substrate potential of said transistor is connected to saidsubstrate bias power source.
 7. A semiconductor IC unit in accordancewith claim 1, wherein said substrate bias controlling circuit outputssaid control signal, then detects that said control signal returned viasaid main circuit has reached a predetermined voltage, therebygenerating a detecting signal.